1. Field of the Invention
The present invention relates to a method for amplifying and demodulating amplitude-modulated signals that includes the steps of: amplification of a primary signal into an amplified signal, bandpass filtering of the amplified signal into a filtered signal, comparison of the filtered signal with a regulation threshold and regulation of the gain of the primary signal such that peak values of the filtered signal approach the regulation threshold, and comparison of the filtered signal with a signal threshold and demodulation of the result of the comparison.
In its device aspect, the invention relates to a circuit for processing amplitude-modulated signals, having an amplifier that creates an amplified signal from a primary signal, having a bandpass filter that creates a filtered signal from the amplified signal, having a regulation comparator that compares the filtered signal with a regulation threshold, having a regulator that regulates a gain of the amplifier such that peak values of the filtered signal approach the regulation threshold, having a signal comparator that compares the filtered signal with a signal threshold, and having a demodulator that demodulates the result of the comparison.
2. Description of the Background Art
Infrared (IR) receiver modules, in particular, typically have a monolithic circuit and an external photodiode. A received infrared signal is amplified, filtered, demodulated and provided at an output as an electrical signal. As a result of the internally provided regulation, the circuit is adapted to ambient conditions. The ambient conditions are affected by such factors as the brightness of the surroundings, in some cases by interfering radiation in the IR frequency range from neon tubes, and the proximity of a data transmitter. Typical data transmitters include, for example, mobile parts of a TV remote control. In the prior art regulation, the signal threshold is greater than the regulation threshold.
For example, data protocols with high data rates and short burst spacings in the protocol frequently cause the threshold value to be exceeded, which then reduces the gain. As a result, it is possible that the smaller signal threshold will no longer be reached. Consequently, these data protocols are thus interpreted as noise to some extent, and suppressed.
Under some circumstances, an approaching data transmitter with a high data rate can cause a similar reaction in the regulation. Here, too, the data from the data transmitter can no longer be demodulated because the regulation triggered by the regulating threshold interprets the data transmitter as an interference source and reduces the gain of the system.
Moreover, the prior art regulating methods are relatively sluggish, so that the output signal of the circuit has undesirably large variation (jitter, output pulse dispersion) with widely varying input data signal strength. For example, the input data signal strength in typical commercial IR remote controls can vary because they are designed to be usable over distances between one centimeter and approximately 35 meters; with their constant radiated power, this results in the aforementioned significant variations in signal strength at the input of the receiver module.